A tropical cyclone is a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has a closed low-level circulation. Tropical cyclones rotate counterclockwise in the Northern Hemisphere. The Atlantic hurricane season runs from June 1st to November 30th, however, these storms can develop before or after the season.
Conditions Which Must Be Present in the Development of a Tropical Cyclone
- Low-pressure system
- Warm temperatures over the Ocean
- Moist environment (precipitation)
- Tropical wind patterns over the equator
Anatomy of a Hurricane:
Hurricanes are a triple threat bringing high winds, soaking rain, and flying debris. Hurricanes can cause devastation and property destruction on a massive scale, making proper disaster mitigation and well-planned response all the more important. While all coastal areas are at risk for hurricanes, Louisiana is particularly vulnerable.
In addition, hurricanes are capable of causing flooding and damage hundreds of miles inland.
- Eye: The eye is the "hole" at the center of the storm. Winds are light in this area. Skies are partly cloudy, and sometimes even clear.
- Eye wall: The eye wall is a ring of thunderstorms. These storms swirl around the eye. The wall is where winds are strongest and rain is heaviest.
- Rain bands: Bands of clouds and rain go far out from a hurricane's eye wall. These bands stretch for hundreds of miles. They contain thunderstorms and sometimes tornadoes.
- H-hour: When 39 mph winds reach the coastline of Louisiana.
Tropical Cyclone Terms
Tropical Depression: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 38 mph (33 knot) or less.
Tropical Storm: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 39 mph (34 knots) to 73 mph (63 knots).
Hurricane: A tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 74 mph (64 knots) or more.
Storm Surge: An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide. Storm surge can reach heights well over 20 feet and can span hundreds of miles of coastline. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Storm surges are the most deadly portion of a hurricane, having caused 50 percent of the fatalities from hurricanes from 1963 to 2012.